Taking an ultra-supercritical unit as an example, with the help of the Ebsilon Professional power station system design software of the German STEAG power station energy company, the simulation research of the constant power variable pressure operation of the steam turbine unit is carried out, and the heat consumption rate of the unit under different initial pressures in the constant power feasible valve position interval is presented. continuous trend of change. Compared with the thermal economic characteristics of variable pressure, the thermal economic characteristics of variable valve position are more suitable for showing the inherent laws of variable pressure operation of nozzle steam distribution units.